I. Field of the Invention
The present invention relates to digital communication protocols. More particularly, the present invention relates to a novel and improved communication protocol between a communication device such as a portable wireless telephone, and an external accessory such as a hands-free kit.
II. Description of the Related Art
In the art of digital audio processing, an audio band encoder/decoder (CODEC) is typically used to convert analog audio signals to encoded digital signals, and vice-versa. For example, the CODEC may receive the analog output of a microphone, and convert the microphone-generated analog audio signal into a Pulse Code Modulation (PCM) encoded digital audio signal for further digital signal processing in a digital signal processor (DSP). Additionally, the CODEC may receive a PCM-encoded digital audio signal from the DSP and convert it to an analog audio signal for use by an audio speaker. Of course, the CODEC may use additional digital encoding techniques as are known in the art, such as A-law, .mu.-law, or the like, or may merely use any other linear or non-linear encoding techniques.
A typical portable radiotelephone having an internal CODEC may be interfaced with one or more external accessories. For example, the portable radiotelephone user may desire to use his portable radiotelephone in his car while driving, and thus interface it with a hands-free speakerphone, a power booster, and/or a voice-operated dialer or voice recognition system. The hands-free speakerphone (or hands-free "kit") allows the user to make phone calls, via an external loudspeaker and microphone, without holding the radiotelephone, leaving the user's hands free to drive the car. The power booster couples radio frequency (RF) signal to and from the portable radiotelephone's own antenna, amplifying the RF signal for the higher power transmission and reception that is desirable when operating off of a car battery. A voice dialer responds to verbal commands from the user. For example, dialing from a set of preprogrammed telephone numbers according to the voice commands, dialing individual digits one at a time, or changing the operating mode of the radiotelephone. These accessories are often used at the same time as part of a car adapter kit.
A typical interface circuit between a portable radiotelephone and an external car kit is given in co-pending U.S. patent application Ser. No. 08/593,305, entitled "PORTABLE COMMUNICATION DEVICE AND ACCESSORY SYSTEM", filed Jan. 31, 1996, assigned to the assignee of the present invention and incorporated herein by reference. The just-mentioned application discloses a portable communications device and accessory system which enables both voice and control commands to be communicated between a portable communication device and external accessories over a single flexible digital interface. When the portable communication device is interfaced to external accessories, such as a power booster and hands-free kit, a microprocessor configures the serial communications bus to pass both the digital voice data and digital control commands to and from the external power booster and the hands-free kit. The external hands-free kit contains its own auxiliary CODEC for encoding analog voice signals and decoding the digital voice data. When the portable communication device is not interfaced with external accessories, the microprocessor configures the serial communication bus to pass the digital voice data to and from an internal CODEC for use with the portable device's own microphone and speaker.
However, there remains a need for a method and apparatus which implements a communication protocol between a portable wireless communication device such as a portable wireless telephone, and an external accessory such as a hands-free kit.